| Автор | Sittler, E. C. |
| Автор | Hartle, R. E. |
| Дата выпуска | 1996 |
| dc.description | We have performed an evaluation to determine whether or not Neptune's magnetospheric electrons can provide the ionization of Triton's ionosphere as previously suggested or whether photoionization is the dominant ionization mechanism. Our approach has been to determine the accessibility of magnetospheric electrons to Triton's ionosphere. Using scaling relationships based on Venus and Titan observations, we have developed estimates of the centrifugal, gradient B and E × B drifts. We have computed trajectories of magnetospheric electrons and studied their accessibility to the Triton ionosphere. The following conclusions can be reached from this study: (1) Centrifugal drift delivers electrons to the ionopause. If centrifugal drift is impaired, then electron precipitation is severely limited. (2) Low‐energy electrons (E < 5 keV) are lost through E×B drift around the ionopause. (3) At higher electron energy the probability of precipitation increases. If the electron gyroradius is small relative to the ionopause thickness, then at pitch angles ∼90° grad B drift dominates with trapping of electrons in the ionopause and subsequent exclusion from the ionosphere. At pitch angles 0° and 180° curvature drift dominates, and electrons will precipitate on entry into the ionopause. If the electron gyroradius is large compared to the ionopause thickness, then electrons will precipitate at any pitch angle. Mass loading is estimated to be unimportant at Triton, and this contributes to the importance of E × B drift and the exclusion of low‐energy electrons to Triton's ionosphere. Our calculations have intentionally overestimated the effects of centrifugal drift to present the best case for electron precipitation. Although collisions are more important for low‐energy electrons (E < 5 keV), we estimate that cross‐field diffusion is small for ionopause heights greater than 725 km. At higher electron energies where collisions are less important, the threshold energy above which electrons become untrapped is only dependent upon the ionopause thickness and not collisions. Pressure balance arguments show that the ionopause is thick with Δz > 200 km. A magnetized ionosphere would be equivalent to the high ram pressure case for the Venus interaction. A thick ionopause would contribute to prevention of precipitation of magnetospheric electrons into Triton's ionosphere when E < 50 keV. Although our calculations at the present level of development cannot rule out the importance of electron precipitation as the source of Triton's ionosphere, we suggest that photoionization be considered viable for the production of Triton's ionosphere. |
| Формат | application.pdf |
| Копирайт | This paper is not subject to U.S. copyright. Published in 1996 by the American Geophysical Union. |
| Тема | IONOSPHERE |
| Тема | Planetary ionospheres |
| Тема | Ionosphere/magnetosphere interactions |
| Тема | MAGNETOSPHERIC PHYSICS |
| Тема | Magnetosphere/ionosphere interactions |
| Тема | Magnetosphere interactions with satellites and rings |
| Тема | Magnetospheric Physics: Magnetosphere—outer |
| Тема | PLANETARY SCIENCES: SOLID SURFACE PLANETS |
| Тема | Ionospheres |
| Тема | PLANETARY SCIENCES: FLUID PLANETS |
| Тема | Ionospheres |
| Тема | PLANETARY SCIENCES: COMETS AND SMALL BODIES |
| Тема | Ionospheres |
| Тема | PLANETARY SCIENCES: SOLAR SYSTEM OBJECTS |
| Тема | Planetology: Solar System Objects: Neptunian satellites |
| Название | Triton's ionospheric source: Electron precipitation or photoionization |
| Тип | article |
| DOI | 10.1029/96JA00398 |
| Electronic ISSN | 2156-2202 |
| Print ISSN | 0148-0227 |
| Журнал | Journal of Geophysical Research: Space Physics |
| Том | 101 |
| Первая страница | 10863 |
| Последняя страница | 10876 |
| Выпуск | A5 |
| Библиографическая ссылка | Banks, P. M., G.Kockarts, Aeronomy Part A, Academic, San Diego, Calif., 1973. |
| Библиографическая ссылка | Bauer, S. J., R. E.Hartle, Venus ionosphere: An interpretation of Mariner 10 observations, Geophys. Res. Lett., 1, 7, 1974. |
| Библиографическая ссылка | Belcher, J. W., et al., Plasma observations near Neptune: Initial results from Voyager 2, Science, 246, 1478, 1989. |
| Библиографическая ссылка | Brace, L. H., H. A.TaylorJr., T. I.Gombosi, A. J.Kliore, W. C.Knudsen, A. F.Nagy, The ionosphere of Venus: Observations and their interpretation, VenusD. M.Hunten, L.Colin, T. M.Donahue, V. I.Moore, 779–840, Univ. of Ariz. Press, Tucson, 1983. |
| Библиографическая ссылка | Bridge, H. S., et al., Plasma observations near Saturn: Initial results from Voyager 1, Science, 212, 217, 1981. |
| Библиографическая ссылка | Broadfoot, A. L., et al., Ultraviolet spectrometer observations of Neptune and Triton, Science, 246, 1459, 1989. |
| Библиографическая ссылка | Cravens, T. E., H.Shinagawa, The ionopause current layer at Venus, J. Geophys. Res., 9611, 119, 1991. |
| Библиографическая ссылка | Cruikshank, D. P., T. C.Owen, T. R.Geballe, B.Schmitt, C.DeBergh, J‐P.Maillard, B. L.Lutz, R. H.Brown, Tentative detection of CO and CO<sub>2</sub> ices on Triton, Bull. Am. Astron. Soc., 23, 1208, 1991. |
| Библиографическая ссылка | Elphic, R. C., C. T.Russell, J. G.Luhmann, F. L.Scarf, L. H.Brace, The Venus ionopause current sheet: Thickness length scale and controlling factors, J. Geophys. Res., 8611, 430, 1981. |
| Библиографическая ссылка | Goertz, C. K., P. A.Deift, Io's interaction with the magnetosphere, Planet. Space Sci., 21, 1349, 1973. |
| Библиографическая ссылка | Hartle, R. E., H. A.TaylorJr., S. J.Bauer, L. H.Brace, C. T.Russell, R. E.DaniellJr., Dynamical response of the dayside ionosphere of Venus to the solar wind, J. Geophys. Res., 85, 7739, 1980. |
| Библиографическая ссылка | Hartle, R. E., E. C.SittlerJr., K. W.Ogilvie, J. D.Scudder, A. J.Lazarus, S. K.Atreya, Titan's ion exosphere observed from Voyager 1, J. Geophys. Res., 87, 1383, 1982. |
| Библиографическая ссылка | Ip, W. H., On the ionosphere of Triton: An evaluation of the magnetospheric electron precipitation and photoionization effects, Geophys. Res. Lett., 17, 1713, 1990. |
| Библиографическая ссылка | Jackson, J. D., Classical Electrodynamics, John Wiley, New York, 1962. |
| Библиографическая ссылка | Jefimenko, O. D., Electricity and Magnetism, Appleton‐Century‐Crofts, New York, 1966. |
| Библиографическая ссылка | Johnson, R. E., Energetic Charged Particle Interactions With Atmospheres and Surfaces, Springer‐Verlag, New York, 1990. |
| Библиографическая ссылка | Knudsen, W. C., C. K.Spenner, P. F.Michelson, R. C.Whitten, K. L.Miller, V.Novak, Suprathermal electron energy distribution within the dayside Venus ionosphere, J. Geophys. Res., 85, 7754, 1980. |
| Библиографическая ссылка | Krall, N. A., A. W.Trivelpiece, Principles of Plasma Physics, McGraw‐Hill, New York, 1973. |
| Библиографическая ссылка | Krasnopolsky, V. A., B. R.Sandel, F.Herbert, R. J.VervackJr., Temperature, N<sub>2</sub>, and N density profiles of Triton's atmosphere: Observations and model, J. Geophys. Res., 98, 3065, 1993. |
| Библиографическая ссылка | Krimigis, S. M., et al., Hot plasma and energetic particles in Neptune's magnetosphere, Science, 246, 1483, 1989. |
| Библиографическая ссылка | Linker, J. A., M. G.Kivelson, R. J.Walker, A three‐dimensional MHD simulation of plasma flow past Io, J. Geophys. Res., 9621, 037, 1991. |
| Библиографическая ссылка | Lyons, J. R., Y. L.Yung, M.Allen, Solar control of the upper atmosphere of Triton, Science, 256, 204, 1992. |
| Библиографическая ссылка | Maclennan, C. G., L. J.Lanzerotti, S. M.Krimigis, R. P.Lepping, N. F.Ness, Effects of Titan on trapped particles in Saturn's magnetosphere, J. Geophys. Res., 87, 1411, 1982. |
| Библиографическая ссылка | Majeed, T., J. C.McConnell, D. F.Stroble, M. E.Summers, The ionosphere of Triton, Geophys. Res. Lett., 17, 1721, 1990. |
| Библиографическая ссылка | Mauk, B. H., E. P.Keath, M.Kane, S. M.Krimigis, A. F.Cheng, M. H.Acuna, T. P.Armstrong, H. F.Ness, The magnetosphere of Neptune: Hot plasmas and energetic particles, J. Geophys. Res., 9619, 061, 1991. |
| Библиографическая ссылка | Ness, N. F., M. H.Acuna, R. P.Lepping, J. E. P.Connerney, K. W.Behannon, L. F.Burlaga, F. M.Neubauer, Magnetic field studies by Voyager 1: Preliminary results at Saturn, Science, 212, 211, 1981. |
| Библиографическая ссылка | Ness, N. F., M. H.Acuna, K. W.Behannon, F. M.Neubauer, The induced magnetosphere of Titan, J. Geophys. Res., 87, 1369, 1982. |
| Библиографическая ссылка | Neubauer, F. M., D. A.Gurnett, J. D.Scudder, R. E.Hartle, Titan's Magnetospheric Interaction, SaturnT.Gehrels, M. S.Mathews, Univ. of Arizona Press, Tucson, 1984. |
| Библиографическая ссылка | Richardson, J. D., J. W.Belcher, M.Zhang, R. L.McNuttJr., Low‐energy ions near Neptune, J. Geophys. Res., 9618, 993, 1991. |
| Библиографическая ссылка | Rossi, B., S.Olbert, Introduction to the Physics of Space, McGraw‐Hill, New York, 1970. |
| Библиографическая ссылка | Russell, C. T., O.Vaisberg, The interaction of the solar wind with Venus, VenusD. M.Hunten, L.Colin, T. M.Donahue, V. I.Moore, 874–940, Univ. of Arizona Press, Tucson, 1983. |
| Библиографическая ссылка | Stevens, M. H., D. F.Strobel, M. E.Summers, R. V.Yelle, On the thermal structure of Triton's thermosphere, Geophys. Res. Lett., 19, 669, 1992. |
| Библиографическая ссылка | Strickland, D. J., D. L.Book, T. P.Coffey, J. A.Fedder, Transport equation techniques for the deposition of auroral electrons, J. Geophys. Res., 81, 2755, 1976. |
| Библиографическая ссылка | Strobel, D. F., M. E.Summers, Neptune/Triton BookDaleCruikshank, Univ. of Arizona Press, Tucson, 1995. |
| Библиографическая ссылка | Strobel, D. F., A. F.Cheng, M. E.Summers, D. J.Strickl, Magnetospheric interaction with Triton's ionosphere, Geophys. Res. Lett., 17, 1661, 1990. |
| Библиографическая ссылка | Summers, M. E., D. F.Strobel, Triton's atmosphere: A source of N and H for Neptune's magnetosphere, Geophys. Res. Lett., 18, 2309, 1991. |
| Библиографическая ссылка | Tyler, G. L., et al., Voyager radio science observations of Neptune and Triton, Science, 246, 1466, 1989. |
| Библиографическая ссылка | Wolf‐Gladrow, D. A., F. M.Neubauer, M.Lussem, Io's interaction with the plasma torus: A self‐consistent model, J. Geophys. Res., 92, 9949, 1987. |
| Библиографическая ссылка | Yung, Y. L., J. R.Lyons, Triton: Topside ionosphere and nitrogen escape, Geophys. Res. Lett., 17, 1717, 1990. |
| Библиографическая ссылка | Zhang, M., J. D.Richardson, E. C.SittlerJr., Voyager 2 electron observations in the magnetosphere of Neptune, J. Geophys. Res., 9619, 085, 1991. |
| Библиографическая ссылка | Zipf, E. C., R. W.McLaughlin, On the dissociation of nitrogen by electron impact and by E.U.V. photo‐absorption, Planet. Space Sci., 26, 449, 1978. |
